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xen-devel
Re: [Xen-devel] Re: [PATCH][v4] PV extension of HVM(hybrid) support in X
On Tuesday 02 March 2010 12:39:34 Jeremy Fitzhardinge wrote:
> On 03/01/2010 07:36 PM, Sheng Yang wrote:
> >> static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
> >> {
> >> u64 delta = native_read_tsc() - shadow->tsc_timestamp;
> >> return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow-
> >> tsc_shift);
> >> }
> >
> > tsc_timestamp take the vcpu beginning at 0, so that's the assumption.
>
> Why would it be 0? Xen sets tsc_timestamp to the current tsc when it
> updates the time parameters, which is whenever the vcpu is scheduled on
> a pcpu (and other times). There's no expectation that the tsc starts
> from 0, since that won't ever be the case.
>
Sorry, I misunderstood. HVM assume it start from 0... PV is following the
native. We set the offset to 0, so that PV tsc is the same as native.
--
regards
Yang, Sheng
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